Some turbochargers utilize semi-floating dual film journal bearings to take advantage of the high tolerance of these bearings to the imbalances in the rotor system. Sometimes, a journal bearing is integrated with a thrust bearing for a compact design and to use the same oil feed and drain passage. These types of bearings may be heavy-duty bearings with the ability to support axial and/or radial loads of the rotor in the turbochargers.
These types of journal bearings, however, need specific mechanical boundary conditions to allow the journal bearing to move or float in the radial direction, while being prevented from rotation and also restrained in the axial direction. In order to provide such a complicated mechanical boundary condition, additional parts or fasteners may need to be added to the turbocharger. These parts are part of the bearing design in the turbocharger to prevent or restrict movement of the journal bearings.
For the benefits achieved by adding a semi-floating journal bearing to a turbocharger, adding new parts to the turbocharger also introduces problems. For example, the new parts add additional points of failure of the turbocharger, may require longer time to install on a turbocharger, can increase the cost of the turbocharger, and/or can make it more difficult or costly to retrofit an existing turbocharger with the semi-floating journal bearing.